Auxiliary fuel supply system

Abstract

An auxiliary fuel supply system is provided for a two cycle internal combustion engine (302). A first fuel line (350) supplies fuel from the fuel pump (338) to a solenoid (352) which is continuously cyclable between ON and OFF states during running of the engine, includig high speed operation where detonation may occur. Fuel then flows through a second fuel line (354) to a restriction orifice metering housing (356), and then to a plurality of third branch fuel lines (358, 384, 386, 388, 390 and 392) for delivery to respective cylinders. The restriction orifices provide a pressure drop from the second fuel line to the plurality of third fuel lines, to provide lower fuel pressure in the third fuel lines, to reduce the chance of leakage at the intake manifold (326), and also to reduce fuel pressure fluctuations in the third fuel lines otherwise due to cycling of the solenoid. Metering housing structure is disclosed. The solenoid is controlled by a variable duty cycle oscillator (408), which in turn is controlled by a fuel enrichment signal (84) output by an electronic control which is responsive to engine knock and/or temperature. Control circuitry is disclosed.

We claim: 
     
       1. A two cycle internal combustion engine having a fuel pump drawing fuel from a fuel tank, comprising: a piston reciprocal in a cylinder between a crankcase and a combustion chamber;   said piston having a charging stroke in one direction compressing fuel-air mixture in said combustion chamber and creating a vacuum in said crankcase, and having a power stroke upon combustion of said mixture driving said piston in the opposite direction pressurizing said crankcase and forcing fuel-air mixture to flow from said crankcase through said transfer passage means to said combustion chamber for repetition of the cycle;   carburetor means receiving fuel from said fuel pump and supplying fuel to said intake manifold;   auxiliary fuel enrichment means comprising:   a first fuel line having an inlet connected to said fuel pump, and having an outlet;   a control valve connected to said outlet of said first fuel line, said control valve having an OFF state blocking fuel flow from said first fuel line, said control valve having an ON state passing fuel flow from said first fuel line, said control valve being operable between said ON and OFF states during running of said engine, including high speed operation where detonation may occur;   a second fuel line having an inlet connected to said control valve, and having an outlet, said control valve blocking fuel flow from said first fuel line to said second fuel line in said OFF state, said control valve passing fuel flow from said first fuel line to said second fuel line in said ON state;   metering orifice means connected to said outlet of said second fuel line and having a giver restriction orifice metering fuel flow;   a third fuel line having an inlet connected to said metering orifice means and receiving fuel flow across said restriction orifice from said second fuel line, said restriction orfice providing a pressure drop thereacross from said second fuel line to said third fuel line to provide lower fuel pressure in said third fuel line and reducing fuel pressure fluctuations in said third fuel line otherwise due to cycling of said control valve between said ON and OFF states, said third fuel line having an outlet connected to said intake manifold to supply extra fuel thereto, said reduced fuel pressure in said third fuel line reducing the chance of fuel leakage at said intake manifold, said control valve being variably cycled between said ON and OFF states and providing a continuous uninterrupted supply of fuel in said third fuel line during all engine operation, said cycling of said control valve limiting and controlling the rate of fuel flow through said third fuel line.   
     
     
       2. The invention according to claim 1 wherein said carburetor means includes a fuel flow orifice, and wherein said restriction orifice of said metering orifice means is smaller than said carburetor fuel flow orifice. 
     
     
       3. The invention according to claim 2 comprising a 150 micron filter immediately downstream of said fuel pump, and a 75 micron filter immediately upstream of said restriction orfice of said metering orifice means. 
     
     
       4. The invention according to claim 1 wherein said engine comprises a multicylinder engine, and wherein said metering orifice means comprises an integral housing having an inlet connected to said outlet of said second fuel line, said housing having a plurality of outlets, one for each cylinder, and comprising a plurality of said third fuel lines, one for each said cylinder, each of said outlets of said housing being connected to a respective said inlet of a respective one of said third fuel lines. 
     
     
       5. The invention according to claim 4 wherein said housing defines an internal plenum common to said housing inlet and each of said housing outlets. 
     
     
       6. The invention according to claim 5 comprising fuel filter means mounted in said housing within said plenum such that fuel flow from said housing inlet to said housing outlets passes through said filter means. 
     
     
       7. The invention according to claim 4 wherein said metering orifice means is provided by said housing outlets, each said housing outlet having said given restriction orifice for its respective said third fuel line. 
     
     
       8. The invention according to claim 1 comprising: transducer means sensing audio signals indicative of engine combustion and occuring within said combustion chamber of said engine and converting said audio signals into an electrical output voltage including a portion representing background noise a portion representing detonation;   electronic control means responsive to said electrical output voltage from said transducer means representing detonation, and outputting a fuel enrichment signal, said control valve being responsive to said fuel enrichment signal.   
     
     
       9. The invention according to claim 8 comprising fail-safe and idle override means responsive to loss of said transducer output voltage to provide said fuel enrichment signal in a fail-safe mode, and responsive to engine speed below a given speed and preventing said fail-safe mode even if a low amplitude transducer output voltage, corresponding to low amplitude audio signals at idle, appears to be a loss of said transducer output voltage. 
     
     
       10. The invention according to claim 8 comprising second transducer means sensing engine temperature and converting engine temperature into an electrical output voltage, and wherein said electronic control means is also responsive to said second transducer means and outputs said fuel enrichment signal to said control valve according to engine temperature, to supply additional fuel when said engine is cold. 
     
     
       11. The invention according to claim 10 wherein said engine includes a battery and a start switch for applying battery voltage to crank and start said engine, wherein said second transducer means comprises a thermistor, and comprising: a voltage source biasing said thermistor such that the voltage across said thermistor varies with engine themperature and provides an output fuel enrichment signal;   means connecting said battery through said start switch to said thermistor such that battery voltage additionally biases said thermistor during cranking of the engine.   
     
     
       12. The invention according to claim 1 comprising: free running variable duty cycle oscillator means connected to said control valve and having a cycle with an ON portion actuating said control valve to said ON state, and an OFF portion actuating said control valve to said OFF state;   means outputting a fuel mixture signal to said variable duty cycle oscillator means and varying the duty cycle thereof.   
     
     
       13. The invention according to claim 12 comprising semiconductor switch means controlling actuation of said control valve, and wherein said variable duty cycle oscillator means comprises a comparator having a first input from said means outputting said fuel mixture signal, and having an output controlling conduction of said semiconductor switch means. 
     
     
       14. The invention according to claim 1 comprising: means responsive to a given engine parameter and outputting a fuel enrichment signal;   free running variable duty cycle oscillator means responsive to said fuel enrichment signal and having a cycle with an ON portion actuating said control valve to said ON state and having an OFF portion acturating said control valve to said OFF state.   
     
     
       15. The invention according to claim 14 wherein said control valve comprises a solenoid continuously cyclicable having a pair of main terminals connected in series with said solenoid for completing a circuit therethrough from a voltage source when said transistor means is conductive, said transistor means having a control terminal for biasing said transistor means into conduction, and wherein said varible duty cycle oscillator means is connected to said control terminal of said transistor means and biases the latter into conduction during said ON portion of said cycle, and wherein said transistor means is nonconductive during said OFF portion of said cycle. 
     
     
       16. The invention according to claim 15 wherein said variable duty cycle oscillator means comprises a comparator having an output connected to said control terminal of said transistor means, and having a first input receiving said fuel enrichment signal, and having a second input connected to a capacitor which is charged by said output of said comparator through a first resistor connected from said output of said comparator to a node betwen said capacitor and said second input of said comparator, and comprising voltage limiting means connected to said node to limit the voltage at said second input of said comparator, said second input of said comparator providing a reference determined by the charge on said capacitor for comparison against said first input of said comparator such that said output of said comparator transitions high when the voltage at said first input of said comparator exceeds the voltage at said second input of said comparator, and such that said output of said comparator transitions low when the charge on said capacitor and the voltage at said second input of said comparator exceeds the voltage at said first input of said comparator, and such that when the fuel enrichment voltage at said first input of said comparator exceeds a give value, said output of said comparator remains high because said voltage limiting means prevents the voltage at said second input of said comparator means from exceeding that at said first input of said comparator means, such that said transistor means remains conductive and said solenoid remains in said ON state and does not cycle to said OFF state, to provide maximum fuel enrichment.   
     
     
       17. The invention according to claim 16 comprising a second resistor connected in series with a diode, said series connected second resistor and siad diode being connected in parallel with said first resistor from said node to said output of said comparator, such that said comparator charges from said output of said comparator through said first resistor, and discharges through said second resistor and said diode to said output of said comparator, and comprising second voltage dropping means connected between said first input of said comparator and said second output of said comparator such that when the charge on said capacitor and the voltage at said second input of said comparator exceeds the voltage at said first input of said comparator and said output of said comparator transitions low, said voltage dropping means lowers the voltage at said first input of said comparator to a given voltage difference above the voltage at said output of said comparator such that said capacitor must discharge to a level below said lowered voltage of said first input of said comparator before said output of said comparator can again transition high. 
     
     
       18. The invention according to claim 17 comprising a positive temperature coefficient thermistor connected in series between said solenoid and said transistor means, said thermistor being heated by excessive current flow therethrough to a blocking condition to block current flow through said transistor means to protect the latter from a defective or shorted solenoid. 
     
     
       19. The invention according to claim 18 wherein said solenoid has a first terminal connected to a battery, and a second terminal connected through a second diode and said thermistor to said transistor means, said second terminal of said solenoid also being connected through a third diode to said battery, such that when said transistor means is ON, current flows from said battery through said solenoid and said second diode and second thermistor, and when said transistor means turns OFF, inductive current from said solenoid flows through said third diode to said battery, to limit said inductive current during cycling of said solenoid. 
     
     
       20. The invention according to claim 14 comprising in combination: transducer means sensing audio signals indicative of engine combustion and occuring within said combustion chamber and converting said audio signals into an electrical output voltage including a portion representing background noise and a portion representing detonation;   means for adjusting the amplitude of said transducer output voltage;   means sampling said portion of said transducer output voltage representing background noise and controlling said adjusting means to decrease the amplitude of said transducer output voltage for increased sensed background noise and to increase the amplitude of said transducer output voltage for decreased sensed background noise;   detonation threshold means responsive to a predetermined increase in the amplitude of said portion of said transducer output voltage representing detonation above the amplitude of said portion of said transducer output voltage representing background noise, and outputting a fuel enrichment signal to an output node;   a thermistor connected to said output node and sensing engine temperature;   a voltage source biasing said thermistor such that the voltage across said thermistor varies with engine temperature and provides an output fuel enrichment signal at said output node;   first isolation means isolating said fuel enrichment signal of said detonation threshold means from said thermistor and said voltage source;   second isolation means isolating said fuel enrichment signal of said thermistor and said voltage source from said detonation threshold means;   said first isolation means comprising a first diode connected in series aiding relation from said detonation threshold means to said output node and passing the fuel enrichment signal from said detonation threshold means to said output node and blocking passage of the fuel enrichment signal from said output node to said detonation threshold means;   said second isolation means comprising a second diode connected in series aiding relation from a node between said thermistor and said voltage source to said output node, and passing the fuel enrichment signal from said second mentioned node to said output node, and blocking passage of the fuel enrichment signal from said output node to said second;   combination fail-safe and idle override means comprising means responsive to loss of said transducer output voltage to provide a fuel enrichment signal at said output node, and responsive to engine speed below a give speed and preventing said fail-safe mode even if a low amplitude transducer output voltage, corresponding to low amplitude audio signals at idle, appears to be a loss of said transducer output voltage;   third isolation means comprising a third diode connected in series aiding relation from said fail-safe and idle override means to said output node, and passing the fuel enrichment signal from said fail-safe and idle override means to said output node, and blocking passage of the fuel enrichment signal from said output node to said fail-safe and idle override means;   said engine including a battery and a start switch, and comprising means connecting said battery through said start switch to said second node such that battery voltage biases said thermistor during cranking of said engine in addition to the bias from said voltage source, such that during cranking of the engine the voltage across said thermistor providing the fuel enrichment signal to said voltage source, and such that after cranking the fuel enrichment signal through said second diode includes the component from said voltage source but not said battery.   
     
     
       21. The invention according to claim 1 comprising: transducer means sensing audio signals indicative of engine combustion and occuring within said combustion chamber of said engine and converting said audio signals into an electrical output voltage including a portion representing background noise and a portion representing detonation;   electronic control means responsive to said electrical output voltage from said transducer means representing detonation, and outputting a fuel enrichment signal;   free running variable duty cycle oscillator means responsive to said fuel enrichment signal and having a cycle within an ON portion and an OFF portion;   said control valve comprising a solenoid continuously cyclicable between said ON and OFF states;   transistor means having a pair of main terminals connected in series with said solenoid for completing a circuit therethrough from a voltage source when said transistor means is conductive, said transistor means having a control terminal for biasing said transistor means into conduction, and wherein said variable duty cycle oscillator means is connected to said control terminal of said transistor means and biases the latter into conduction during said ON portion of said cycle, and wherein said transistor means is nonconductive during said OFF portion of said cycle.   
     
     
       22. The invention according to claim 21 comprising: fail-safe and idle override means responsive to loss of said transducer output voltage to provide said fuel enrichment signal in a fail-safe mode, and responsive to engine speed below a given speed and preventing said fail-safe mode even if a low amplitude transducer output voltage corresponding to low amplitude audio signals at idle, appears to be a loss of said transducer output voltage;   second transducer means sensing engine temperature and converting engine temperature into an electrical output voltage, and wherein said variable duty cycle oscillator means is responsive to said second transducer means to control conduction of said transistor means and cycling of said solenoid according to engine temperature, to supply additonal fuel to said engine when said engine is cold.